This invention relates to a carrier for carrying at least one sample, and preferably a plurality of samples, containing beta-particle-emitting material to be assayed by means of a scintillation counter, and a scintillant to be contacted with the sample(s).
More especially, the invention relates to such a carrier which comprises a sorption sheet on which the or each sample is to be deposited and a transparent container within which the sorption sheet having the sample deposited thereon is to be introduced.
U.S. Pat. No. 4,298,796 describes a sorption sheet in the form of a filter mat bearing a plurality of samples which is placed in a transparent container adapted to contain a liquid, solid or gel scintillant. When a liquid scintillant is used, there is the danger that the samples might diffuse into the scintillant away from the sample area or might otherwise be displaced by the addition and dispersal of the scintillant when added to the container.
Furthermore, the photons of light produced by the beta-particle emitting material and counted by the scintillant counter have a tendency to pass between samples through the liquid scintillant ("crosstalk").
U.S. Pat. No. 4,298,796 also describes the possibility that the filter mat itself may be composed of a scintillant, for example scintillant glass fibres. However, there would be difficulties associated with the manufacture and maintenance of the physical properties needed for a filter formed of a solid scintillant alone.
In order to minimise diffusion or migration of the samples on the sorption sheet and at the same time minimise optical crosstalk between samples when measured, U.S. Pat. No. 4,728,792 proposed the use of a sorption sheet comprising barriers extending through at least a portion of the thickness of the sheet. When conducting an assay of the beta-particle-emitting samples, the sorption sheet according to that patent is sealed in a transparent bag with enough liquid scintillant to soak the whole sheet. As with the filter mat according to U.S. Pat. No. 4,298,796 the sorption sheet according to U.S. Pat. No. 4,728,792 still requires the use of a quantity of liquid scintillant, although considerably less than when using vials in a conventional liquid scintillation counter. Furthermore, the liquid scintillant has to be spread throughout the mat while in the bag, and this tends to cause cross-contamination of the samples. Besides the aspect of costs, handling liquid scintillants is quite a messy job.